Today a variety of metals are used in the construction of engine components, including the cylinder block and cylinder head. The use of many of these metals, such as aluminum, serves to reduce the total weight of the engine. While many of these metals or alloys have a desirably low mass per unit volume, they may be insufficiently resistant to friction abrasion when used to form parts having relative motion therebetween. For example, the cylinder block may define a cylinder in which a piston reciprocates, the cylinder having an inner surface or wall which is abraded by the piston. Another problem associated with use of these metals or alloys is that they are often susceptible to corrosion or erosion from the oil, fuel and other materials used in the engine.
To protect inner cylinder surfaces, cast iron sleeves (liners) have been installed to make the sliding surface more resistant to abrasion by the piston. These sleeves are heavy, however, and detract from the original goal of creating a lightweight engine.
As a result, one approach to solving the above-stated problems has been to coat or "plate" the sliding surfaces of the engine, such as the inner cylinder surface, with more durable materials such as chrome or nickel. This proposed solution has the advantage that greater durability may be obtained without the weight associated with solutions such as sleeves. On the other hand, plating has several drawbacks and associated problems.
A main problem with plating is associated with casting pits on the surfaces which are to be plated. These pits or holes are generated during the casting process and extend inwardly from the sliding surface of the casting, such as the inner surface of the cylinder. In order to protect the sliding material from erosion and abrasion, as described above, the exposed casting surfaces in these pits must be protected with plating.
As illustrated in FIG. 1, a casting pit b exists in a casting a, such as a cast aluminum cylinder block. When the pit b has a maximum dimension of over about 0.2 mm, it is often difficult to protect the casting surface in the pit in the manner desired. One method of plating which is effective in plating even large dimension pits is to immerse or dip the casting in a plating liquid and apply a differentiating voltage to the casting and liquid. This method is generally effective in creating a plating layer c which extends even into the pit b, covering the casting surfaces defined therein. On the other hand, this method of plating is very slow and is not generally useful when plating in selective locations of the casting is desired.
As a result, methods of high speed plating have been developed. Such high speed plating methods are described in a U.S. Pat. No. 5,647,967 issued Jul. 15, 1997, entitled "Plating Method For Cylinder," U.S. Pat. No. 5,660,704 issued Aug. 26, 1997, entitled "Plating Method and Plating System For Non-homogenous Composite Plating Coating," U.S. Pat. No. 5,520,791 issued May. 28, 1996, entitled "Non-homogenous Composite Plating Coating," U.S. Pat. No. 5,549,086 issued Aug. 27, 1996, entitled "Sliding Contact-Making Structures in Internal Combustion Engine," U.S. Pat. No. 5,619,962 issued Apr. 15, 1997, entitled "Sliding Contact-Making Structures In Internal Combustion Engine," and U.S. Pat. No. 5,666,933 issued Sep. 17, 1997, entitled "Sleeveless Cylinder Block Without Marginal Plating Coating," which are incorporated herein by reference.
In general, in this method a pipe electrode is positioned in the cylinder, the pipe having an outer surface spaced from the inner wall or surface of the cylinder. A voltage is potential is provided between the pipe and cylinder and then plating liquid is delivered in a dispersed substance forming material to the cylinder to or from the pipe. This plating material flows at a relatively high velocity (such as 1 to 7 m/s) along the wall of the cylinder, coating it with plating material.
Use of this high speed plating method is especially effective when the casting pits are less than 0.1 mm in maximum width dimension, as illustrated in FIG. 2(b), in that as the material flows along the inner wall of the cylinder at high speed, the plating material spans or bridges across the opening or top of the pit, effectively sealing the casting surfaces exposed therebelow. As a result, an improved harder sliding surface is provided and the casting surfaces, even in the pit, are protected from corrosion and erosion.
On the other hand, as illustrated in FIG. 2(a), pits having a maximum dimension of over about 0.2 mm are generally not plated. In particular, these larger pits or pores present a stagnation area which is filled with dispersed carrier and then prevents the plating material carried thereby from spanning or filling the void. As such, the exposed casting surface within the pit erodes or corrodes at point d illustrated therein.
A improved plated cylinder and method of creating the same which overcomes the above-stated problems is desired.